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ABSOLUTE CALIBRATION OF THE FOURIER INTERFEROMETRIC TRANSMISSOMETER

The report presents a detailed analysis of the method used to calibrate the Fourier Interferometric Transmissometer (FIT). Derivation of the calibration equation is based on a fundamental relation of radiometry, the radiance conservation law N' = TN. Thus, the calibrated spectrum of atmospheric transmission is simply determined by obtaining the ratio of a source signal to a local reference signal and then correcting it by the calibration factor. In addition, the report discusses an experimental procedure to evaluate the quality of collimating systems used as a source in transmissometers.